Method of and apparatus for electric spot welding



Dec. 31, 1935. Q E HATHORN 2,025,744

METHOD OF AND APPARATUS FOR ELECTRIC SPOT WELDING Filed March 17, 1934 Patented Dec. 3l, 1935 PATENT oFFI/CE METHOD OF AND APPARATUS FOR ELECTRIC SPOT WELDING Charles E. Hathorn, Kenmore, N. Y., assigner to Curtiss Aeroplane & Motor Company, Inc., a corporation of New York Application March 17, 1934, Serial No., 716,016

16 Claims.

' This invention relates to a method of and apparatus for electric spot welding of metal tubes.

The type of tube structure with which the invention is concerned Vcomprises tubular members formed from at sheet metal, the metal strip having flanged edges and the strip being bent into the form of a tube so that the flanges abut each other and extend inwardly from the tube surface. 'Ihis arrangement permits of a smooth exterior 1G tube surface, without projections. Such a tube is particularly useful when made from stainless steel, and when` the tube is designed for use as a structural part of aircraft. To weld the anges of such a tube requires special apparatus, and it 1,; is with this apparatus that the invention is particularly concerned.

I provide an insulating block having a slot therein for tting engagement with the inwardly turned tube anges, the block having electrodes mounted in the slot for contact with said anges. Conductors are led from these electrodes through the tube, or alternately, the electrodes may contact other portions of the inner tube surface. Externally of the tube, members are pressed thereagainst to slightly deform the tube wall and to cause intimate contact between the tube and block. The block is resilient, so that deformation of the tube causes deformation of the block, thus causing the electrodes to intimately contact the inturned tube flanges. Thereupon, a welding current may be passed to the electrodes to spot weld theanges to each other. 4

In practice, each weld may be quickly made, after which the tube is moved with respect to the block and pressure member in readiness for another weld.

Qbjects of the invention are to provide a method of electrically spot welding tubes and other closed members; to provide apparatus for electrically spot welding elements in the interior of tubes or other closed members; to provide a method and apparatus for completing the formation of tubes from strip sheet metal, wherein the outer surface of the resulting tube is free from projecting anges; and to provide a method and apparatus for spot welding interior anges on tubes or closed members having a limited amount of space-therewithin. Anothervobject of the invention is to provide alternative forms of apparatus for accomplishing the above objectives, one embodiment including direct electrical connections to the welding electrodes, and theother including indirect connections to the electrodes.

A more complete understanding of the invention, as well as further objects thereof, may be obtained by referring to the annexed detail description in conjunction with the drawing, in which similar numbers indicate similar parts, and in which:

Fig. 1 is a perspective view, partly broken away, 5v of a tube being welded 4according to the method of the invention;

Fig..2 is a sectional elevation of the tube and apparatus of Fig. 1;

Fig. 3 is a section on the line 3 3 of Fig. 2; 10

Fig. 4 is a section on the line 4 4 of Fig. 2;

Fig. 5 is a side elevation, partly in section, of an alternative apparatus to accomplish the desired welding method; and

Fig. 6 is a section on the line 6-6 of Fig. 5.

The form of member to bewelded is shown as a substantially square tube I0, formed by bending 4a strip of metal into the square form with adequate fillets I I at the corners thereof. The edges of the strip are bent inwardly to form flanges I2 at one corner of the tube, these flanges abutting each other. Upon spot welding of the anges to each other, the tube is complete and presents a relatively smooth outer surface, free from pro- Y trusions. Such a tube may be fabricated from 25 stainless or alloy steels which usually are supplied as fiat sheet, and which are diflicult to procure as drawn or extruded tubing. Likewise, such a tube may be made of very' thin gauge material, whereby great strength with extreme lightness accrue.

To effect welding of the ilanges I2, a block I3 of insulating material is shaped to slide loosely within the tube I0, said block having lower surfaces I4 contacting the lower inner surfaces of the tube, and having upper. surfaces I5 loosely contacting the upper inner surfaces of the tube on each side of the anges I2. The block I3 is slotted at I6, the anges I2 fitting within the slot. A pair of electrodes I1 is-tted into a suitable recess in the block I3, one of the pair on each side of the slot I6, and these are arranged to establish a restricted Welding contact with the anges I2, at I8. Each electrode is also organized to contact the inner tube wall at I9, adjacent the flanges I2, for the supply of welding current to the point of welding, as will be more fully pointed out hereinafter. A rod 20 is xed to the block I3 and extends parallel to the tube I 0, the rod serving as a handle for moving the block I3 50 along the tube as successive welds are made.

A lower grooved block 2| is mounted on a base 22, the groove being arranged to receive the lower corner of the tube I0. An upper grooved block 23 is fixed to a reciprocating press-plunger 24, 55

i of tube I0. Here, electrodes 3l carried by the the upper tube faces together, -and to press theflanges I2 toward each other. Also, by such pressure, the upper portions of the block I3, by virtue of the slot IS and the resiliency of the block material, are pressed into rm contact with the flanges I2, the electrodes I'I having good contact with the anges and with inner surfaces ofthe tube wall.

The block 23 is provided with a pair of contact elements 25 which, when the plunger is pressed down, contact the outer tube surfaces at points opposite to the points of contact of the electrodes- II therewith. A pair of cables 26 are attached to the,contact pieces 25, and lead to the conventional welding transformer.

In operation, assuming copper contact pieces and electrodes, and stainless steel alloy for the tube I0, and the broad welding method wherein high amperage welding current eifects the weld in a timed interval of a small fraction of a second, the welding current passes from the contact pieces 25 through the tube wall to the electrodes, the passage of current at this stage oifering little heating effect to the tube sheet due to the relatively large area of contact. The welding current passing between the electrodes II must pass through the restricted portion I8 tat the flanges, whereby the ange weld is effected. As the specific resistance of the stainless steel is quite high,

-but little of the welding current is by-passed around the portion to be welded through the tube proper. i

Figs. 5 and 6 show an alternative arrangement of the welding blocks applied to the same form block I3', andspaced by the slot I6', are connected directly to the welding transformer by exible cables 32, snap connectors 33 effecting the cable-electrode connection. The electrodes are insulated by the insulating-material of the block I3', from Contact with any portion of the tube Ill except at the anges I2 where the weld is to be made. The upper and lower pressure blocks 2 I and 23', and their function in the welding process, are the same as described in connection withthe rst embodiment. however, the block 23 is homogeneous and requires no contact pieces.

In using the apparatus, the blocks I3, 2| and 23 may be mounted in vertical alignment, the rod 20 holding the block I3. The tube I0 may be moved along the blocks and a series of closely spaced welds may be made with a minimum of trouble.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled inthe art, after understanding my invention, that various changes and modications may be made therein without departing from the spirit or scope thereof. I aim in the appendedclaims to cover al1 such modifications and changes.

What is claimed is:

1. Apparatus for spot Welding inwardly bent anges of a formed tube comprising a bifurcated member insertable Within the tube and having its bifurcations straddling adjacent anges, contact pieces carried by said member for contact with said anges, and means for causing said In this case,`

contact pieces to bear under pressure on said iianges comprising an externally applied member having elements engageable with portions of said tube on the inner surface of which said bifurcations are in contact.

r2. In apparatus for welding inturned anges of a tube,a member adapted to be inserted within said tube, said member having portions bearing on the inner tube walls and having contact pieces bearing on opposite faces of the flanges to be welded, means externally of said tube for pressing on the outer faces of said tube opposite vthe bearing points of said member on the inner face of said tube, and electrical connections to each of said contact pieces.

3. The method of welding together inturned anges of a tube formed from sheet metal which comprises inserting a pair of electrodes within the tube so that one electrode is'in electrical contact with each of the pair of flanges, each said electrode having contact with the inner surfaces of said tube, then applying pressure externally of said tube at points opposite to the point of Ycontact of said electrodes with the inner surface of said tube, whereby saidelectrodes are pressed against said flanges, and then applying a welding currentv through said electrodes.

4. Apparatus for Welding the l'inturned flanges of a strip of metal formed as a tube, said tube being of substantially rectangular conformation and having said flanges at a corner thereof, comprising a block insertable Within said tube and having faces engaging the inner surface of the several side -faces thereof, electrodes carried by saidblock for contact Withan opposed face of each said flange, means for making an electric welding circuit through said electrodes and flanges, and means bearing on the outer surface of said tube at points opposite to those points at which said block engages the inner surfaces of trode loosely engaging the element to be welded,

and means bearing .on the outer surface of said flexible member at points opposite the bearing points of said block on the inner surface thereof; said bearing means being arranged to press on said member to thus cause, by deformation oi said iiexible member, intimate engagement of said block with the inner surface of said member and of said electrode with the element to be welded.

y 6. Means for electrically welding elements 'within and forming part of a hollow member comprising a block Within said member, means for pressing said member with its elements against said block, and means for passing a Welding current through said hollow member. and elements.

7. Means for electrically welding edges. of a hollow member formed from sheet material, comprising a block insertable within said member, an electrode carried by said block and contacting an inner surface of said hollow member, and a second electrode organized to be pressed against said hollow member opposite to the point of contact of said first electrode therewith.

8. Means for electrically welding edges of a Cal hollow member formed from sheet material, comprising a block insertable within said membenand bearingon a portion of the inner surface thereof, an electrode carried by said block and adapted to engage a portion of the inner surface of said member opposite to that portion engaged by said block, and means for pressing externally on said member to effect intimate contact between said electrode and said member.

9. Means for electrically welding inturned edge flanges of a sheet metal strip formed as a tube, said flanges, when welded, serving to complete the closure of said tube, comprising a slotted block insertable Within said tube, said anges engaging within said slot, electrodes carried by said block and forming the bounding surfaces of said slot whereby said electrodes contact said anges, means for establishing electrical connections with said electrodes, and means acting externally upon said tube for deforming same to bear on said block and to establish intimate contact between said tube and said block.

l0. Means for electrically welding inturned edge flanges of a sheet metal strip formed as a tube, said flanges when welded serving to complete the closure of said tube, comprising a slotted block insertable within said tube and loosely contacting opposed faces of said tube, electrodes forming the inner surfaces of .said slot for contacting said edge flanges, said electrodes extending to an outer surface of said block to contact an inner surface of said tube, and a grooved member engageable under pressure with the outer surface of said tube, said member having contact pieces contacting said tube at points opposite the points of contact of said electrodes with the inner surfaces of said tube whereby welding current for welding said flanges passes through said contact pieces, said tube and said electrodes.

11. Means for electrically welding a pair of elements to each other comprising an electrode adapted to press against each said element opposite the point at which the weld is to be eiected, and to bear at another point on each said elenient,v and means organized to bear upon each said element opposite said other point at which each said electrode bears on each said element, by which pressure imposed on saidA means is passed through said element, and to said electrode, to hold said electrode in intimate pressure contact with said element.

12. In means for welding a pair of lelements to each other, an electrode on one'side of said element, bearing thereon at a point adjacent the weld point and at another point relatively remote from said weld point, and means pressing on the opposite side of said element adjacent said other trode with said element at both said points.

13. Means for resistance welding a metal ele ment having an acute bend therein, the weld point being spaced from the apex of said bend,

. comprising an electrode embraced by saidbent element and bearing on the metal faces adjacent said electrode having a portion piece to be welded is closely spaced to a second- .point for effecting intimate contact of said elecpiece, and wherein said pieces are relatively mov able in slight degree, an electrode inserted b'etween said pieces and bearing upon both, said electrode contacting said rst named piece at the point to be welded, and means bearing upon said second piece on the side thereof opposite to' that side with which said electrode engages, said means being pressable upon said second piece to move it, and to thus movethe electrode into intimate contact with said first piece.

15. In means for resistance welding wherein a piece to be welded is closely spaced to a second piece, and wherein said pieces are relatively movable in slight degree, an electrode inserted between said pieces and bearing upon both, said electrode contacting said rst named piece at the point to be welded, means bearing upon said second piece on the side thereof opposite to that side with which said electrode engages, said means being pressable upon said second piece to move it, and to thus move the electrode into intimate contact with said rst piece, and an electric welding connection to said pressable means by which current iiows therefrom through said second piece, and through said electrode by virtue of its intimate contact therewith, to said welding point.

16. In means for welding one element to a second element, said second element comprising spaced apart pieces, one of which is to be welded to said rst element, and the normal space between said pieces being reducible by deflection of said pieces, a flller block carrying an electrode insertable within said space and having clearance from said pieces, and means for causing intimate contact of said electrode with the piece to bev welded comprising a member bearing on the outside of the other said piece and adapted to cause intimate contact of both said pieces with said filler block by deection of said pieces.

CHARLES E. HATHORN. 

